The invention relates to a method for the preparation of relief structures by phototechniques from mixtures containing olefinically unsaturated polymers and azides as photo initiators.
One of the most accurate structuring methods for insulating materials, semiconductor and conductor materials in electrical engineering is the phototechnique. Here, resist relief structures generated by phototechniques are copied on substrates by suitable processes such as etching, vapor deposition and electroless or electroplating metallization. Resist relief structures can furthermore take over permanent protection functions, for instance, as insulation.
In a method know from U.S. Pat. No. 3,957,512 and U.S. Pat. No. Re. 30,186, both incorporated herein by reference, relief structures are made from highly heat-resistant polymers. To this end, radiation-sensitive soluble preliminary polymers in the form of a layer or foil are applied to a substrate; the radiation-sensitive layer or foil is then irradiated through negative patterns; and subsequently, the non-irradiated layer or foil portions are removed from the substrate. If necessary, this can be followed by tempering or annealing of the relief structure obtained. In this method, polyaddition or polycondensation products of polyfunctional carbocyclic or heterocyclic compounds carrying radiation-sensitive radicals with diamines, diisocyanates, bis-acid chlorides or dicarboxylic acids are used as soluble preliminary polymers. The compounds carrying the radiation-sensitive radicals contain two carboxyl, carboxylic-acid chloride, amino, isocyanate or hydroxyl groups suitable for addition or condensation reactions, and, partially in ortho- or peri-position thereto, radiation-reactive groups bound to carboxyl groups as esters. According to U.S. Pat. No. Re. 30,186, these radiation-reactive groups are oxyalkylene-acrylate or oxyalkylene-methacrylate groups.
The light sensitivity of resist materials such as photoreactive polymers can be increased further by the addition of photo-initiators and photo-sensitizers. This is important because the economics of structuring of surfaces by phototechniques dictate that the time for which the expensive exposure devices are used be as brief as possible, i.e., the sensitivity of the photoresists used is as high as possible. In the known method, compounds such as Michler's ketone, i.e., 4,4'-bis(dimethylamino)-benzophenone, benzoine ether, 2-tert-butyl-9,10-anthraquinone; 1,2-benz-9,10-anthraquinone and bis(diethylamino)benzophenone are added to the preliminary polymer stages for this purpose.
It is known to use azides as photo-initiators for resists, especially negative resists, with diallylphthalate prepolymers, polyisoprene resins and polyvinylcinnamates as polymers or preliminary polymers (see: W. S. DeForest, "Photoresist", McGraw-Hill Book Company, 1975, pages 35 to 41). As photo-initiators, generally diazides with the following structure have been used: ##STR1##